Or any tax strategies that I’m potentially missing out on by not setting it up in an LLC versus personal conventional mortgages?

I know private money could possible work

As a mortgage expert, my advice would be to ensure the financing aligns well with your plans and goals.

I currently own a single-family 3/2 in South Philly and the mortgage is about $1,900 a month.

If you are borrowing money, the lender would usually create a property mortgage document and record a lien on your property/land.

That being said, it's going to be very near to impossible to find an investment property that will just cashflow (where the tenants will pay for your mortgage and then some).

Your mortgage person can do it, too.

I don't think private lenders would have this requirement, unless title companies encourage wet sign as standard practice.

I am looking to see what forms and documents to use when borrowing money from a private investor.  

To find investment possibilities, consider elements including property pricing, demand for rentals, vacancy rates, and economic trends.Think About Financing choices: Investigate your choices for financing a possible real estate purchase, such as FHA loans, conventional mortgages, home equity lines of credit, or other innovative financing techniques.